The present invention relates generally to axial flow impellers and more particularly to axial flow energy converters (e.g. fans) utilizing certain impellers.
Axial flow devices, particularly fans, are well-known in the art. One reference text in this art is William C. Osborne, Fans, 2nd Edition (in SI/metric units), 1977, published by Pergamon Press, Inc., Maxwell House, Fairview Park, Elmsford, New York 10523. Particular reference may be made to chapter 2 which describes differing types of fans. The Osborne text is hereby incorporated by reference.
One application of an axial flow fan is in a fluid pumping device incorporated within a clean air hat which pumps air through a filter to a human wearer. In order to provide sufficient purified air to a wearer working in the environment where the hat is being worn, a certain minimum volumetric flow rate of air must be drawn into the hat. To enable the hat to be completely portable, it is desirable that the pumping device (fan) be battery powered. For a hat using batteries, it is preferred that the hat be as light as possible and that it be able to operate as long as posible. An axial flow fan which develops sufficient differential pressure and volumetric flow rate and minimizes battery drain (power consumption) is desirable.
In one axial flow fan designed for a clean air hat marketed under the tradename "Airhat" by Minnesota Mining and Manufacturing Company, a small electric motor is mounted within a shroud with a set of guide vanes. An impeller is attached to the motor shaft and has a central hub and a plurality of blades radially mounted to the edge of the hub with each of the blades set at an attack angle in order to pump fluid (air) through the fan. This axial flow fan exhibits certain performance characteristics of pressure differential and volumetric flow at a certain voltage and amperage (power consumption).
There is desired an axial flow fan which develops improved pressure and volumetric flow and minimizes battery drain (power consumption).